Hi,

Hi mass 30 is usually caused by the following:

1. The oxidation reactor was exposed to oxygen/air when hot

2. The reduction reactor doesn't work properly

3. The filament is oxidized and soon to fail

Regards

Jakov

-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of stableisotopes
Sent: Dienstag, 14. Oktober 2008 19:01
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] mass 30 on a Delta V connected to an EA

David,

It is almost certainly NO from NOx not being completely reduced as the
copper column is being consumed. NO is mass 30 and comes out slightly
after N2 on the GC column.  Our experience is that it doesn't initially
affect the 29/28 ratio but will if it gets bigger.  I would recommend
that you take out the copper column and see how much has been reduced.  
It probably needs replacing.

I have been trying to get manufacturers to start adding QC software that
will stop the analysis if the 30/28 ratio goes over a user adjusted
ratio.  That way if a copper column breaks through during a long run
overnight the system would stop and no samples would be lost.

Hope this helps,

Paul Brooks.


 

Denhaan, David wrote:
> Dear List,
>  
> I've been watching my mass 30 trace evolve from a peak that comes out 
> with 28 and 29 and then begins to tail more and more severely until 
> eventually it migrates into a peak that comes out after 28 and 29 as I

> run more samples.  Is this poor combustion, exhausted copper, or 
> oxygen getting in from a leak?  I ran a blank with and without oxygen 
> injection and I thought I might see a peak come off if the copper was 
> expended but I didn't see any peaks either way.  Whatever is happening

> doesn't appear to be affecting the 29/28 ratio.
>  
> Thanks,
>  
> David
>  
> David DenHaan
> USDA ARS
> National Soil Tilth Laboratory
> 2110 University Blvd.
> Ames Iowa 50011
> 515-294-0118
> [log in to unmask]
>  


--
Mr. Paul D. Brooks,
Dept. Integrative Biology MC3140,
3060 Valley Life Sciences Building,
UC Berkeley, 94720-3140.

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